The invention relates to a light bulb comprising a base to which a filament is linked, which filament is intended to emit a luminous radiation and has turns arranged in spiraling shape around an axis of revolution.
Such a light bulb is marketed by applicant under the reference number PL10044067. The filament in this light bulb is kept in position by means of a single metal support of which one end is fixedly united to the base and of which another end comprises a closed hook which surrounds one of the turns of the filament, said two ends of the support being linked by a rod.
The known light bulb is constructed such that, when the light bulb is in its normal operational position, the rod of the support is situated below the filament. Applicant has observed that the filament, when traversed by a current, has a tendency towards mechanical deformation, developing a curvature which displaces in downward direction the ends of the filament on either side of the hook which keeps said filament in position. Thus several turns may come into contact with the rod of the support, which then leads to a short-circuit which may destroy the support and the filament itself.
The present invention has for its object to avoid all risk of short-circuits due to such a deformation of the filament by proposing a light bulb in which the extent of the deformation of the filament is limited.
To achieve this object, according to the invention, a light bulb as described in the introductory paragraph comprises in addition a plurality of supports, each having an end linked to the base and another end provided with a hook which is in contact with one of the turns of the filament.
The plurality of supports provided in accordance with the invention enables to keep the filament better in position and prevents a simultaneous contacting of several of its turns with one and the same support.
In one of the embodiments of the invention, the hooks are all situated at a same side of the axis of revolution of the filament.
Such an embodiment simplifies the manufacture of the supports, which may thus be formed by a single rod provided with a plurality of hooks. The linking between the supports and the base will also be simplified thereby.
In a special embodiment of the light bulb according to the invention, the supports are designed so as to be situated above the filament when the light bulb is in its normal operating position, and the hooks of the supports are open hooks.
The fact that the hooks are open considerably simplifies the manufacture of the light bulb. Indeed, if the hooks are closed, the filament must be screwed through the eyelets of the hooks, which requires an appreciable amount of time which is reflected in the manufacturing cost of the light bulb. The use of open hooks merely requires the placement of the turns upon the hooks, thus reducing the manufacturing cost of the light bulb.
In a preferred embodiment of the invention, with one end of the filament fixedly united to the base, the other end of the filament is connected to said base via a framework formed by a rod situated within a region inside the turns of the filament and outside a plane defined by the axis of revolution and points of contact between the hooks and the filament, as shown in FIG. 2.
This embodiment of the framework enables to ensure that it (i.e., the framework formed by the rod situated within the region inside the turns of the filament and outside the plane defined by the axis of revolution) will lie outside a path which would be followed by the turns of the filament under the influence of the mechanical deformation observed for the known light bulb, if said turns were not retained in position. Such a choice, therefore, avoids all risk of short-circuits between the filament and the reinforcement element.